Package net.sf.saxon.expr

Class FilterExpression

    • Field Detail

      • doneReorderingPredicates

        public boolean doneReorderingPredicates

      • FILTER_PREDICATE

        public static final OperandRole FILTER_PREDICATE

    • Constructor Detail

      • FilterExpression

        public FilterExpression​(Expression base,
                        Expression filter)
        Constructor
        Parameters:
        base - The base expression to be filtered.
        filter - An expression defining the filter predicate

    • Method Detail

      • setBase

        public void setBase​(Expression base)

      • disableIndexing

        public void disableIndexing()

      • getFilter

        public Expression getFilter()
        Get the filter expression
        Returns:
        the expression acting as the filter predicate

      • setFilter

        public void setFilter​(Expression filter)

      • getExpressionName

        public java.lang.String getExpressionName()
        Get a name identifying the kind of expression, in terms meaningful to a user.
        Overrides:
        getExpressionName in class Expression
        Returns:
        a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.

      • getItemType

        public ItemType getItemType()
        Get the data type of the items returned
        Specified by:
        getItemType in class Expression
        Returns:
        an integer representing the data type

      • getStaticUType

        public UType getStaticUType​(UType contextItemType)
        Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.
        Overrides:
        getStaticUType in class Expression
        Parameters:
        contextItemType - the static type of the context item
        Returns:
        the static item type of the expression according to the XSLT 3.0 defined rules

      • isFilterIsPositional

        public boolean isFilterIsPositional()
        Ask if the filter is positional
        Returns:
        true filter is positional

      • getActionExpression

        public Expression getActionExpression()
        Get the subexpression that is evaluated in the new context
        Specified by:
        getActionExpression in interface ContextSwitchingExpression
        Returns:
        the subexpression evaluated in the context set by the controlling expression

      • isPositional

        public boolean isPositional​(TypeHierarchy th)
        Determine if the filter is positional
        Parameters:
        th - the Type Hierarchy (for cached access to type information)
        Returns:
        true if the value of the filter depends on the position of the item against which it is evaluated

      • isSimpleBooleanFilter

        public boolean isSimpleBooleanFilter()
        Test if the filter always returns a singleton boolean.

        This information is available only after typeCheck() has been called.

        Returns:
        true if the filter is a simple boolean expression

      • isIndependentFilter

        public boolean isIndependentFilter()
        Determine whether the filter is independent of the context item and position

        This information is available only after typeCheck() has been called.

        Returns:
        true if the filter is a numeric value that does not depend on the context item or position

      • typeCheck

        public Expression typeCheck​(ExpressionVisitor visitor,
                            ContextItemStaticInfo contextInfo)
                     throws XPathException
        Type-check the expression
        Overrides:
        typeCheck in class BinaryExpression
        Parameters:
        visitor - the expression visitor
        contextInfo - return the expression after type-checking (potentially modified to add run-time checks and/or conversions)
        Returns:
        the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
        Throws:
        XPathException - if an error is discovered during this phase (typically a type error)

      • optimize

        public Expression optimize​(ExpressionVisitor visitor,
                           ContextItemStaticInfo contextItemType)
                    throws XPathException
        Perform optimisation of an expression and its subexpressions.

        This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

        Overrides:
        optimize in class BinaryExpression
        Parameters:
        visitor - an expression visitor
        contextItemType - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE
        Returns:
        the original expression, rewritten if appropriate to optimize execution
        Throws:
        XPathException - if an error is discovered during this phase (typically a type error)

      • getCost

        public double getCost()
        Return the estimated cost of evaluating an expression. This is a very crude measure based on the syntactic form of the expression (we have no knowledge of data values). We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one), and we assume that a sequence has length 5. The resulting estimates may be used, for example, to reorder the predicates in a filter expression so cheaper predicates are evaluated first.
        Overrides:
        getCost in class Expression
        Returns:
        the estimated cost

      • getIntegerBounds

        public IntegerValue[] getIntegerBounds()
        For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis. The default implementation returns null, meaning "unknown" or "not applicable". Other implementations return an array of two IntegerValue objects, representing the lower and upper bounds respectively. The values UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH are used to indicate values limited by the size of a string or the size of a sequence.
        Overrides:
        getIntegerBounds in class Expression
        Returns:
        the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.

      • addToPathMap

        public PathMap.PathMapNodeSet addToPathMap​(PathMap pathMap,
                                           PathMap.PathMapNodeSet pathMapNodeSet)
        Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.
        Overrides:
        addToPathMap in class Expression
        Parameters:
        pathMap - the PathMap to which the expression should be added
        pathMapNodeSet - the PathMapNodeSet to which the paths embodied in this expression should be added
        Returns:
        the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression

      • unordered

        public Expression unordered​(boolean retainAllNodes,
                            boolean forStreaming)
                     throws XPathException
        Replace this expression by a simpler expression that delivers the results without regard to order.
        Overrides:
        unordered in class Expression
        Parameters:
        retainAllNodes - set to true if the result must contain exactly the same nodes as the original; set to false if the result can eliminate (or introduce) duplicates.
        forStreaming - set to true if optimizing for streaming
        Returns:
        an expression that delivers the same nodes in a more convenient order
        Throws:
        XPathException - if the rewrite fails

      • isPositionalFilter

        public static boolean isPositionalFilter​(Expression exp,
                                         TypeHierarchy th)
        Determine whether an expression, when used as a filter, is potentially positional; that is, where it either contains a call on position() or last(), or where it is capable of returning a numeric result.
        Parameters:
        exp - the expression to be examined
        th - the type hierarchy cache
        Returns:
        true if the expression depends on position() or last() explicitly or implicitly

      • computeCardinality

        protected int computeCardinality()
        Get the static cardinality of this expression
        Overrides:
        computeCardinality in class BinaryExpression
        Returns:
        the cardinality. The method attempts to determine the case where the filter predicate is guaranteed to select at most one item from the sequence being filtered

      • computeSpecialProperties

        protected int computeSpecialProperties()
        Get the static properties of this expression (other than its type). The result is bit-significant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.
        Overrides:
        computeSpecialProperties in class BinaryExpression
        Returns:
        the static properties of the expression, as a bit-significant value

      • equals

        public boolean equals​(java.lang.Object other)
        Is this expression the same as another expression?
        Overrides:
        equals in class BinaryExpression
        Parameters:
        other - the expression to be compared with this one
        Returns:
        true if the two expressions are statically equivalent

      • computeHashCode

        protected int computeHashCode()
        get HashCode for comparing two expressions
        Overrides:
        computeHashCode in class BinaryExpression
        Returns:
        the hash code

      • copy

        public Expression copy​(RebindingMap rebindings)
        Copy an expression. This makes a deep copy.
        Specified by:
        copy in class Expression
        Parameters:
        rebindings - a mutable list of (old binding, new binding) pairs that is used to update the bindings held in any local variable references that are copied.
        Returns:
        the copy of the original expression

      • getStreamerName

        public java.lang.String getStreamerName()
        Get the (partial) name of a class that supports streaming of this kind of expression
        Overrides:
        getStreamerName in class Expression
        Returns:
        the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class

      • toString

        public java.lang.String toString()
        The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax
        Overrides:
        toString in class BinaryExpression
        Returns:
        the expression as a string in XPath 3.0 syntax

      • toShortString

        public java.lang.String toShortString()
        Description copied from class: Expression
        Produce a short string identifying the expression for use in error messages
        Overrides:
        toShortString in class BinaryExpression
        Returns:
        a short string, sufficient to identify the expression

      • export

        public void export​(ExpressionPresenter out)
            throws XPathException
        Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
        Specified by:
        export in interface ExportAgent
        Overrides:
        export in class BinaryExpression
        Parameters:
        out - the ExpressionPresenter to be used
        Throws:
        XPathException - if the export fails, for example if an expression is found that won't work in the target environment.

      • setFlags

        public void setFlags​(java.lang.String flags)

      • getElaborator

        public Elaborator getElaborator()
        Make an elaborator for this expression
        Overrides:
        getElaborator in class Expression
        Returns:
        a suitable elaborator